1. Field of the Invention
The present invention relates to a process for producing a p-halogenobenzophenone derivative useful as a monomer for heat-resistant polymers.
2. Description of the Related Arts
p-Halogenobenzophenone derivatives are recently especially noted as monomers for heat-resistant polymers such as polyether ketones and polythioether ketones and a development of a process for producing them at a low cost is eagerly demanded. Known processes for producing halogenobenzophenone derivatives include those wherein a halogenobenzene is directly acylated, such as (1) a process wherein chlorobenzoyl chloride is reacted with a halogenobenzene, (2) a process wherein a halogenobenzene is reacted with phosgene (see European Patent No. 147,299), and (3) a process wherein chlorobenzene is reacted with carbon monoxide (see Japanese Patent Laid-Open No. 221146/1986), as well as a process wherein a 1,1-dichloro-2,2-bis(halogenopheny)ethylene is oxidized with nitric acid, a process wherein p-chlorobenzotrichloride is reacted with chlorobenzene in the presence of a Lewis acid catalyst such as iron chloride or aluminum chloride (see French Patent No. 2,534,906) and a process wherein the reaction is conducted in the presence of a crystalline aluminosilicate (see Japanese Patent Laid-Open No. 121945/1990).
However, the above-described prior art processes have problems. Namely, the process wherein a halogenobenzene is directly acylated with phosgene or carbon monoxide is unfavorable to be conducted on an industrial scale, since phosgene and carbon monoxide are chemicals having a strong toxicity. The process wherein a 1,1-dichloro-2,2-bis(halogenophenyl)ethylene is oxidized with nitric acid has a problem in the production per se of the starting material, since the production of the starting material causes environmental pollution. Further the process wherein chlorobenzene is directly acylated with an acid chloride in the presence of a Lewis acid and the process wherein p-chlorobenzotrichloride is reacted with chlorobenzene in the presence of a Lewis acid catalyst such as iron chloride or aluminum chloride have a problem of catalyst removal and a problem of waste water treatment. Namely, when a Lewis acid catalyst soluble in the reaction system, such as iron chloride or aluminum chloride, is used, the whole reaction liquid must be washed with an acid and water after the completion of the reaction so that the catalyst migrates into the aqueous layer. This necessitates a complicated operation and, in addition, water used in a large quantity for washing posed a problem of environmental pollution if it is discharged as it is.
Although the process wherein p-chlorobenzotrichloride is reacted with chlorobenzene in the presence of crystalline aluminosilicate (zeolite) is a preferred process free from the above-described problems, it is yet unsatisfactory for conducting on an industrial scale, since the life of the catalyst is short and a complicated catalyst regeneration is necessary for the repeated use. In particular, the recovery of the activity thereof is slight when it is washed with a solvent and the conversion is sharply reduced when this catalyst is repeatedly used after mere washing with the solvent. Thus when zeolite is repeatedly used as the catalyst, a problem is posed that it must be frequently regenerated by heat treatment or the like.
Thus all the prior art processes involve problems when they are conducted on an industrial scale.